1. Field of the Invention
The present invention relates generally to heating appliances or appliances intended to be heated during the use thereof and comprising a self-cleaning coating.
2. Description of Related Art
The term “heating appliance” is understood to mean, within the meaning of the present patent application, any appliance, article or utensil, which, during the functioning thereof, reaches a temperature at least equal to 65° C. (which is the minimum reheating temperature) and preferably at least equal to 90° C. The appliance can reach this operating temperature by means which are specific to it, such as, for example, a heating base incorporated in the appliance and equipped with heating elements, or by external means. It concerns in particular sole plates of irons, cooking appliances, ovens, grills and cooking utensils. Among these heating appliances, some, such as sole plates of irons or cooking appliances, exhibit qualities of ease of use and effectiveness which depend, inter alia, on the state and the nature of the surface of the coating thereof. As regards sole plates of irons, the latter have been able to be improved by virtue of the care contributed to the glide qualities of the ironing surface, in combination with those which make possible easier spreading of the laundry. One way of obtaining these qualities is to resort to sole plates enameled with an enamel having a smooth appearance, optionally with lines of excessive thickness for promoting the spreading of the fabric during the movement of the iron. It is also known to use metal sole plates which are treated mechanically and/or which are or are not covered with a deposit for facilitating the gliding.
However, with use, the sole plate can become tarnished by carbonizing in a more or less diffuse fashion over its ironing surface, and, in a more or less incomplete fashion, various contaminants of organic origin (in particular in a particulate form) which are captured by the sole plate by rubbing over the ironed fabrics. The tarnishing of the sole plate, even in a not very visible way, results in an at least partial loss of its glide qualities. In addition, with the fouling, ironing becomes more difficult. Finally, the user dreads using a tarnished iron, fearing that it may detrimentally affect her laundry.
Iron sole plate coatings, comprising a hard and resistant layer covered by a layer which improves the surface properties, are known, such as taught by the U.S. Pat. No. 4,862,609. However, this patent does not indicate a solution for combating fouling.
This problem of fouling may also be encountered for other types of heating appliances, such as, for example, the walls of cooking appliances. It is known to cover them with an enameled layer having a smooth appearance, in order to prevent possible spat fat or food from adhering to the surface of these walls. In particular, enameled self-cleaning surfaces, which may in particular be encountered in ovens and cooking utensils, are known, such as taught, for example, by U.S. Pat. No. 4,029,603 or French patent FR 2 400 876. However, these surfaces are not entirely satisfactory as regards their self-cleaning properties.
In order to improve these properties, the Applicant Company has previously developed a self-cleaning coating intended to coat a metal surface of a heating appliance which is more effective in terms of catalytic activity. This coating forms the subject matter of the French patent FR 2 848 290, which describes a heating appliance comprising a metal support, at least a portion of which is covered with a self-cleaning coating, which comprises an external layer in contact with the ambient air and comprising at least one oxidation catalyst chosen from platinum group metal oxides, and at least one internal layer, located between the metal support and the external layer, comprising at least one oxidation catalyst chosen from oxides of the transition elements of Group Ib. However, this self-cleaning coating exhibits the disadvantage of requiring a large amount of platinum group metal oxides in the external layer in order to achieve correctly satisfactory levels of catalytic activity, the consequence of which is in particular a significant increase in the coating cost and thus, in the end, in that of the heating appliance.